The news last week that Rep. Jimmy Duncan would not seek re-election means that 12 current Republican U.S. House members have announced they are calling it quits in 2018.

The departure of the incumbents is unlikely to have on impact on the Republican majority in the House. In nearly all the dozen GOP-held seats that are open, Republicans are strong bets for retention.

Former Rep. Tom Davis R-Va., past chairman of the National Republican Congressional Committee, told me, “Watch the swing districts. So far [Minnesota Democrat Tim] Waltz and [Florida Republican Rep.] Ileana Ros-Lehtinen are they only retirees from swing districts. They balance each other out.”

Since 1866, the 2nd District (Knoxville) represented by Duncan has been in Republican hands without interruption. Since 1950, its U.S. Representative has been named Baker (Howard H. Baker Sr., namesake-father of the future Senate Majority Leader, held it from 1950 until his death in 1963, when his term was filled out by wife Irene) or Duncan (John Duncan held it from 1964 until his death in 1988, whereupon Jimmy won it in a special election).

But the question of why lawmakers from the ruling party would voluntarily relinquish “safe” districts is increasingly coming up in official Washington. Political veterans as well as political scientists are divided on the reason.

“I’m just not sure,” Michael Barone, syndicated columnist for the Washington Examiner and co-founder of “The Almanac of American Politics,” told Newsmax. “Congressman Duncan was very unhappy with the ‘neo-con’ [interventionist] foreign policy. And at age 70 after 30 years in Congress, he may just be tired.”

Barone’s view was echoed by historian Donald Critchlow of Arizona State University, author of "Future Right: The Forging of a New Republican Majority." Duncan’s departure, Critchlow told me, “is perfectly normal. He’s been in Congress forever.”

“Jimmy may have concluded what I did at age 68,” said former National Republican Congressional Committee Chairman John Linder. “It’s time to let new blood come in with new energy and enthusiasm. I wouldn’t read much into this.”

But there are other opinions about the meaning of Duncan’s departure and those of other “safe” Republicans.

“As Bob Dylan put it, ‘the times they are a changin,' and so is life in Congress,” said David Pietrusza, author of five books on presidential election years. “A greater need to fundraise — even in safe districts — the nastiness of town hall meetings, talk radio, and the Internet, and the burden of constant travel back-and-forth to home districts make holding a congressional seat less like an honor than a sentence.”

Pietrusza also pointed out that “because the GOP de jure ‘controls’ all branches of the federal government, Republican voters expect instant action on their agenda. They are, however, forgetting to do the math on what constitutes a very slender Republican majority in what is a very cumbersome legislative body — the United States Senate. The mantra is that Republicans had seven years to plot how to repeal and replace Obamacare. True enough, but Democrats had nearly 50 years to go from Harry Truman's call for national health insurance plan to Obamacare. And it took huge Democratic majorities in the House and Senate to effect Obamacare.

“The Republican Party today does not enjoy such huge majorities. The agenda cannot be easily passed. The voters rebel. And members of Congress share their frustration.”

John Gizzi is chief political columnist and White House correspondent for Newsmax. For more of his reports, Go Here Now.